In wireless communication applications, various signal formats are utilized to transfer both voice signals as well as data signals. In a typical wireless communication system, such as a cellular system, a plurality of base stations utilizing transceivers with RF amplifiers are used to transceive signals with a plurality of mobile devices, such as cellular phones. Traditionally, such wireless communications were focused upon the transmission of voice signals as telephonic applications drove the earliest needs for such systems. However, data applications have become more prevalent such that it is desirable that a base station be able to adequately handle both voice signals and data signals in their various forms.
In more modern wireless communication protocols, such as CDMA (Code Division Multiple Access) systems, it is desirable to monitor and control the output power of the base station RF amplifiers, as well as the linearity of such amplifiers. CDMA applications are particularly sensitive to non-linearities and power levels. Therefore, in current RF amplifier design, the bias currents of the various amplifier stages in the RF line (which are typically A/B amplifier stages) are controlled to minimize interference between the various channels of the system. The amplifier performance is commonly referred to as Adjacent Channel Leakage performance (ACPR).
Generally, a low Adjacent Channel Leakage is desirable to yield the best ACPR performance of the system. As noted above, voice signals have traditionally dominated wireless communication applications, whereas, data signal transmission is currently increasing. Conventionally, the bias currents of a typical RF amplifier at a base station have been adjusted for the best ACPR performance when the amplifier is working with and amplifying voice signals, which are considered non-pulsed input signals. That is, the amplifier is optimized for non-pulsed voice signals or a non-pulsed condition. However, data signals are pulsed signals and present a pulsed signal condition to the amplifier.
Specifically, one such example is a CDMA High Data Rate (HDR) signal. The transmission of such pulsed data signals through amplifiers that are optimized for non-pulsed voice signals leads to degraded performance. More specifically, the amplifiers become more non-linear under pulsed signal conditions because of the amplifier's increased gain expansion when operated under such pulsed conditions. This leads to a non-optimum ACPR performance (6-8 dB higher emissions) under such pulsed signal conditions.
In some products, a pulsed input signal is detected by means of an input RMS detector, an envelope detector and high-speed A/D converter, and a Field Programmable Gate Array (FPGA) integrated circuit. The input RMS detector is used to determine the average value of the input signal. The envelope detector and A/D are used to determine the peak value of the input signal. The FPGA is programmed to calculate the peak-to-average ratio of the input signal, and, based on this information, it determines if the input signal is pulsed.
There is still a need to provide an improved and low cost amplifier that can detect the presence of a pulsed RF signal that is applied to the amplifier, such as when this type of signal information is not available from the base station, or when the above mentioned components are not incorporated in the amplifier due to cost constraints. There is further need to improve amplifier performance and linearity for handling a variety of different signals that are amplified and transmitted, such as at a base station. Also, there is a need to ensure proper performance of the amplifier for both voice and data signals.